CVD reactors in the semiconductor processing field serve to deposit a layer of material on the surface of a substrate formed of a material such as silicon. One form of such reactors deposit a hetero-or homoepitaxial layer of monocrystalline silicon on a wafer of monocrystalline silicon. The layer can be provided with a dopant to convert the layer to an N-type semiconductor with, for example, phosphorus or a P-type semiconductor with boron. A conventional reactor using chemical vapor as the agent to deposit the epitaxial layer is termed a chemical vapor deposition (CVD) reactor. Several steps are needed to achieve the final deposition layer, each step being at a different temperature than the other steps. For this reason separate compartments or sections of the reactor are needed to provide the different temperature conditions of the several steps of the process. Accordingly, seals are used to isolate the chamber from the external ambient during each step of the process.
Many CVD reactor chambers have been proposed using fluid cooled elastomer seals to achieve the desired isolation of the chambers. While such seals have proved adequate for low or moderate temperature polycrystalline CVD deposition of silicon, silicon oxide, or silicon nitride, they have not been successful in use for high temperature production of silicon epitaxial devices.
Several continuous vapor deposition reactors have been proposed. For example, see U.S. Pat. No. 4,048,955 entitled CONTINUOUS CHEMICAL VAPOR DEPOSITION REACTOR BY R. N. Anderson, issued on Sept. 20, 1977. This patent describes a reactor having a plurality of chambers that are separated from each other along the path of movement of wafers passing therethrough by the use of elastomer seals to achieve the desired isolation of one chamber section from the other. The quartz reactor chambers of this patent are joined to one another by multi-ported fluid cooled, flanged junctions sealed with silicon rubber. The junctions include directed gas streams that are used to separate the atmosphere in the various adjacent CVD deposition chambers. The difficulty with the use of this type of reactor is that silicon wafers, for example, must pass through the fluid cooled junctions at high temperatures, that is, temperatures greater than 1120.degree. C., the minimum temperature required for conventional silicon epitaxial growth. The wafers are then exposed to the cold gases exiting from the junctions onto the wafers. The wafers as they pass through the cold junctions cannot be sustained at the required heat by infrared lamps. The operation of the isolation junctions require very small passage clearances for the wafers and their carriers, such clearances being in the order of 1 mm. Using hydrogen carrier gas which is typically used for epitaxial deposition and the practical materials used in such reactor construction, it appears that the junctions will either be overheated or that the silicon wafers would be under-cooled as they pass through each of the isolation junctions. Another disadvantage of the system of the Anderson U.S. Pat. No. 4,048,955 is that it requires infrared heating. Induction or resistance heating cannot be used without interfering with the correct use of the reactor junctions.
See, also, U.S. Pat. No. 3,672,948 entitled METHOD FOR DIFFUSION LIMITED MASS TRANSPORT by R. A. Foehring, et al. issued on June 27, 1972. This patent discloses a continuous reactor having a single chamber through which a carrier for substrates is passed during the deposition process steps. The various gases used during the process are passed into the chamber across the movement direction of the wafers. It seems that the gas flow across the wafer movement produces inherently non-uniform deposits, as seen from the growth rate curves of FIG. 5 of the patent, since the material in the gas is depleted across the wafers. Moreover, a system such as that of the patent, using the perforated or porous members, can easily clog and cause frequent shut-downs. In addition, such porous members, being formed of quartz, are very fragile. If such members are formed of metal, then the chemical source gas containing chlorine can react with the metal and develop contaminants to harm the substrates or wafers being processed.
Prior art continuous chemical vapor deposition reactors are not known to be used in production for silicon epitaxial devices. The reason for this, seemingly, is that single crystal epitaxial devices grown in such reactors cannot tolerate any leakage of the atmosphere, external from the reactor, or any out-gassing of the elastomer seals which might result from deterioration due to prolonged use at excessive temperatures. Amorphous and polycrystalline growth of silicon, silicon oxide and silicon nitride can be accomplished in the temperature range of approximately 350.degree. to 900.degree. C. In contrast, silicon epitaxial temperatures commonly used in production are in the range 1050.degree. to 1250.degree. C. Except for very special applications using silane at 960.degree.-1000.degree. C. the preferred minimum temperature for silicon epitaxial growth is 1120.degree. C. to 1140.degree. C. using other silicon halide gases as a source material which is sometimes termed a "gaseous phase material," or a "chemical source gas stream."
It is clear there is a need in the art for an improved CVD reactor for epitaxial growth of silicon useful in solid state device structures.